The present invention relates to a conveyor belt cleaner and tensioning arrangement, and in particular to a conveyor belt cleaner and tensioning arrangement wherein the scraper blades of the conveyor belt cleaner have a blade face which provides initial and subsequent full-face contact with the conveyor belt and wherein the scraper blades maintain a substantially constant cleaning angle with the surface of the conveyor belt and engage the conveyor belt with a substantially constant scraping pressure during the wear life of the scraper blades.
Conveyor mechanisms utilize an endless conveyor belt to transport bulk material, such as sand, gravel, coal and other bulk materials, from one location to another. Such a conveyor utilizes a rotating drum at each end of the moving belt. As the bulk material is discharged from the moving conveyor belt, a portion of the bulk material often remains adhered to the outer surface of the conveyor belt. Conveyor belt cleaners, including one or more scraper blades, are used to scrape the adherent material from the belt on its return run and thereby clean the belt. The scraper blades of a conveyor belt cleaner are removably attached to a rotatable cross shaft that extends transversely across the width of the conveyor belt. A tensioning device is attached to the cross shaft and applies a rotational biasing force to the cross shaft which in turn rotates the tips of the scraper blades into scraping engagement with the conveyor belt.
Scraper blades were previously made such that just the scraping edge of the blade face surface initially engaged the conveyor belt, rather than the entire or full blade face surface, when installed. This edge contact type of blade design cleans with high efficiency when new, but after the blade wears for a short period of time cleaning effectiveness is lost. Scraper blades that provide full-face contact between the face surface of the blade and the conveyor belt, such as those of the present invention, can be designed to maintain constant cleaning efficiency over their wear life. Full-face contact blades extend the life of the of the blade, particularly on high speed conveyors because a full-face contact blade has more mass to absorb the heat of friction generated with the rotating belt. Full-face blades also eliminate a problem known as feathering which occurs with primary cleaner blades when just the scraping edge engages the belt.
The present invention also enables a scraper blade to operate with a substantially constant cleaning angle and scraping pressure. The tips of primary scraper blades engage the curved surface of the conveyor belt at the head pulley of the conveyor and form a cleaning angle between the conveyor belt surface and the front surface of the scraper blade at the scraping edge of the front surface. The tip of each scraper blade also includes a scraping surface that engages the surface of the conveyor belt. The scraping surface engages the surface of the conveyor belt with a scraping pressure that is approximately equal to the scraping force with which the scraper blade engages the conveyor belt divided by the area of the scraping surface of the scraper blade.
During operation, the scraping edge and the scraping surface of each scraper blade wears due to its scraping engagement with the rotating conveyor belt. The tensioner rotates the cross shaft and the scraper blades to maintain the scraper blades in biased scraping engagement with the conveyor belt. As the scraper blades wear and are rotated into continuing engagement with the conveyor belt, the orientation of the scraper blades with respect to the conveyor belt changes, which typically causes a change in the cleaning angle between the surface of the conveyor belt and the front surface of the scraper blade at the scraping edge, and a change in the scraping pressure with which the scraper blade engages the conveyor belt. In order to maintain optimum cleaning of the surface of the conveyor belt, and to achieve maximum scraper blade life and performance, the cleaning angle between the scraper blades and the conveyor belt surface, and the scraping pressure with which the scraper blades engage the conveyor belt, should remain substantially constant during the wear life of the scraper blades as the scraper blades wear and are rotated into continuing engagement with the conveyor belt. One approach to partially solving this problem is shown in U.S. Pat. No. 4,917,231 owned by the applicant herein.
A conveyor belt cleaner and tensioning arrangement including a conveyor belt cleaner and a tensioner. The conveyor belt cleaner includes a cross shaft having a central axis. One or more scraper blades are mounted on the cross shaft. The cross shaft and the scraper blades are selectively rotatable about the central axis. The tensioner includes a mounting member attached to the cross shaft for conjoint rotation with the cross shaft. The tensioner also includes a resilient biasing member, such as a spring, and an actuator member, such as turnbuckle. The actuator member and the biasing member are operatively attached to one another. The actuator member and the biasing member operatively attach the mounting member to a stationary member.
Operation of the actuator member causes the conveyor belt cleaner cross shaft and the attached scraper blades to rotate about the central axis. Once the conveyor belt cleaner scraper blades are rotated into full-face scraping engagement with the conveyor belt, further operation of the actuator member changes the length of the biasing member and thereby stores a biasing force within the biasing member. As the scraper blades wear, the biasing member causes the cross shaft to rotate and thereby maintains the scraper blades in full face contact with the conveyor belt. The magnitude of the biasing force provided by the biasing member decreases as the scraper blades wear, and the distance between the central axis about which the scraper blades rotate and the tips of the scraper blades which engage the conveyor belt also decreases, thereby changing the force with which the scraper blades are biased into engagement with the conveyor belt. The area of the blade face scraping surface changes as the scraper blades wear to account for the change in the force with which the scraper blades are biased into engagement with the conveyor belt such that the contact pressure between the scraper blades and the conveyor belt remains substantially constant as the scraper blades wear and as the biasing member continues to rotate the scraper blades into engagement with the belt.